1. Field of the Invention
The present invention relates in general to a support structure installed in a motor vehicle, and more particularly to a center member structure designed to carry thereon an engine unit of the motor vehicle.
2. Description of the Prior Art
Many of the modern motor vehicles are of a frameless type. In the vehicles of such type, a center member structure is commonly employed which is designed to carry the engine unit thereon. Usually, the center member structure extends along the longitudinal axis of the vehicle and has both ends secured to axially spaced portions of a body of the vehicle respectively. In order to carry thereon the heavy engine unit, very high strength is required by the center member structure.
One of the conventional center member structures is shown in FIGS. 17 and 18 of the accompanying drawings. The structure comprises a longitudinally curved channel member 2 and a longitudinally curved plate member 4 which are spot-welded to constitute a longitudinally curved hollow structure. A reinforcing member 6 is attached to the inner surface of the channel member 2 to increase the mechanical strength of the structure. Numerals 5 denote the portions to which the spot welding is practically applied.
However, the center member structure of such coventional type has the following several drawbacks due to its inherent construction.
First, since the parts, viz., the channel member 2 and the plate member 4, of the structure are of a fair-sized pressed member, large-sized and thus expensive press machines are necessary.
Second, since a considerably large area of the structure needs to be welded to obtain a robust construction, the welding process requires a long time and thus correspondingly increases the production cost of the structure.
Third, it is difficult to accommodate the design change of the parts of the structure because of using large-sized press machines. In fact, any design change of the parts requires preparation of a new mold or molds which are expensive. Thus, hitherto, it has sometimes occurred that overstrengthened parts are employed for a center member structure to which only a small load is applied in practical use. This is wasteful.
Fourth, it has sometimes occured that the mutually contacting portions of the members 2 and 4 are painted poorly because of the numerous portions to which the welding is applied.
Fifth, as is understood from FIG. 19, when a large lead is applied to the center member structure, for instance at the time the motor vehicle is jacked up, the contacting portions 7 of the members 2 and 4 tend to separate thereby affecting the resiliency and rigidity of the center member structure.